Planet in a Bottle

Phil Plait writes Slate’s Bad Astronomy blog and is an astronomer, public speaker, science evangelizer, and author of Death From the Skies!

It may not feel like it, but they’re there. Sunlight travels across space and hits the Earth. Some is absorbed, some reflects away. The ground heats up, warming the air above it. That air rises. The rotating Earth swings the air sideways. Turbulence causes eddies, vortices. The air picks up dust, blows it around, evaporates water that eventually rains out, carries smoke from fires across the globe.

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All of this is due to the laws of physics, which operate using the language of math. These laws are understood, they can be written down, and computers can be programmed to apply them. Sitting in Greenbelt, Md., at NASA’s Goddard Space Flight Center—my old stomping grounds, in fact—is one such supercomputer, trained in the ways of the math and physics of the Earth’s surface, water, and atmosphere. And when it’s done cranking through the calculations, it can produce things like this:

This is not a photo of the Earth from some far-flung satellite. This is the output of a computer that has been programmed to take those laws of physics and apply them to the Earth. It has data about sunlight hitting the Earth (which includes variations for season); it knows about the composition of the Earth’s atmosphere and how the air’s temperature changes with latitude, longitude, and height; it can calculate how much water evaporates and where it rains or snows out; it accounts for fires, dust, the Earth’s rotation, the local geography, and even humanity's effect on the environment.

And when it’s done, it can show us what the Earth looks like under various conditions. In this case, the blue swirls over the oceans trace sea salt; green is smoke from forest fires, white is sulfate particles (emitted from volcanoes and the burning of fossil fuels), and reddish-orange is dust blown about.

That last bit is amazing. In the US, we’re used to the overall wind patterns blowing west-to-east, but that’s not the case everywhere. Over northern Africa, the wind blows west, and it can pick up surface dust and transport it thousands of kilometers over the Atlantic. In the summer of 2012, so much Saharan dust blew over Florida it actually caused a haze in the sky which obscured distant objects.

But pay attention to the white swirls as well. Man-made emission of some particles equals or outweighs volcanic eruptions (for example, humans dump 100 times more carbon dioxide into the atmosphere every year than volcanoes do), including sulfates from coal burning. Overall, sulfates help cool the Earth, so tracking them is important — but we also know the effect is not as strong as heating from greenhouse gases.

Computer models like the one used at Goddard show us how these effects play out. If it gets unusually hot over one region, rainfall might increase in another. A fire might change the transparency of the air, blocking sunlight, cooling an area covering thousands of square kilometers. Clouds forming in one place might affect the way fresh water flows into the ocean from rivers, changing the salt content there, and that can drastically change the way water circulates in the oceans, which in turn affects how heat from the equator is transferred to the poles (and how cold water flows from the poles to the equator).

The Earth is an enormous feedback mechanism, every part affecting every other. Computer models like this are a powerful tool in understanding the intricacies of how this fiendishly complex system behaves. And it’s models like this that show us how human activity is warming our globe.

The pictures above are incredibly beautiful, despite being computer simulations. But their true beauty lies in what they reveal about our planet, informing us of our effect on it. These models work, because math and science work. And they tell us the Earth is getting hotter, that weather patterns will change, that our Arctic ice will shrink more, and that sea levels will rise.

Reality is as it is, and the math and science are telling us this. It’s well past time everyone listened.